Effect of pH and stream order on iron and arsenic speciation in boreal catchments
- Author(s)
- E. Neubauer, S.J. Köhler, F. Von Der Kammer, H. Laudon, Thilo Hofmann
- Abstract
Riverine transport of iron (Fe) and arsenic (As) is affected by their associations with natural organic matter (NOM) and suspended iron (oxy)hydroxides. Speciation has a strong influence on element transport from the headwaters to the ocean because NOM may be transported over longer distances compared to iron (oxy)hydroxides. We show that Fe speciation changes along the flow path of a boreal watercourse, as water moves from NOM-rich, acidic first-order streams with pH as low as 3.9 to less acidic higher-order systems (up to pH 6.4). Analysis by Flow Field-Flow Fractionation and chemical equilibrium modeling revealed that Fe from wetland-dominated headwaters was mainly exported as Fe-NOM complexes; in catchments with a stream order >1 and with higher pH, Fe was present in Fe-NOM complexes and precipitated as nanoparticulate iron(oxy)hydroxides which aggregated as the pH increased, with their size eventually exceeding the membrane filters cutoff (0.2 μm). The measured NOM-bound Fe decreased with increasing pH, from 0.38 to 0.16 mmol Fe·g. The high concentrations of NOM-bound Fe emphasize the importance of boreal catchments to Fe export to the oceans. Concentrations of As in the 4.5 became associated with iron(oxy)hydroxides, and its transport thus became more coupled to that of the iron(oxy)hydroxides downstream in the circumneutral streams.
- Organisation(s)
- External organisation(s)
- Swedish University of Agricultural Sciences (SLU)
- Journal
- Environmental Science & Technology
- Volume
- 47
- Pages
- 7120-7128
- No. of pages
- 9
- ISSN
- 0013-936X
- DOI
- https://doi.org/10.1021/es401193j
- Publication date
- 07-2013
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105302 Hydrochemistry, 104002 Analytical chemistry, 104023 Environmental chemistry, 105904 Environmental research
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/1b5fa3d6-d357-4012-adc0-fca7291fd1c9